Although conventional steels with crystalline structure, containing various carbon levels, have been extensively utilized by industries, bulk amorphous steels having glassy microstructure show great potential to supercede crystalline steels for some structural and functional applications due to their superior properties, such as higher strength, better magnetic properties and better corrosion resistance. For example, some known bulk Fe based amorphous alloys have shown a hardness of above HV1200, which is twice that of the high-grade ultra-high strength steel (e.g. 18Ni Maraging 300).
It was also found that some known ferromagnetic Fe based bulk amorphous alloys have extremely high energy conversion efficiency when used as transformer cores of electrical transformers or other energy conversion devices. As a result, using these materials as cores can save up to ⅔ of total energy loss due to the heat dissipated by distribution transformers and motors with conventional ferromagnetic cores.
Moreover, compared with most of other bulk amorphous alloy systems such as Zr- and Pd-based, bulk amorphous steels also show some superiority: much lower material cost; higher strength; better magnetic properties; and higher thermal stability (glass transition temperature is close to or above 900 K)
However, one major obstacle to the feasibility of Fe based amorphous steels is their typically low GFA. Although thin ribbons with a thickness of <100 μm have been successfully utilized in many application fields, such limitations have prevented wide spread industrial application thereof.
Significant efforts have been recently devoted to synthesizing Fe-based bulk metallic glasses with enhanced GFA. One composition reported for bulk glass formation in Fe-base alloys containing carbon is Fe43Mo16Cr16C15B10 which can only be cast into a rod with a diameter of 2.5 mm by injecting the molten alloy into a copper mold under high cooling rates and high-vacuum. Hence, it is necessary to improve the GFA of Fe-based alloys in order to enhance the ability thereof to form bulk glassy specimens under conventional industrial conditions, for example, commercial-grade charge materials, low vacuum furnace, conventional casting methods, etc. Thus, such alloys could be more viable for engineering applications.
The patent referenced above describes a new series of bulk amorphous alloys Fe—Zr—Y—(Co, Mo, Cr)—B that still contain significant amounts of costly materials such as Zr and Co. Moreover, the maximum cross-section size of fully glassy samples needs to be as larger. New and improved bulk amorphous alloys are needed which have higher GFA and lower materials costs such that the alloys are more economical and suitable for various applications.